With increases in capacity of information processing in recent years, various information recording techniques have been developed. Particularly, the surface recording density of the HDD using the magnetic recording technique continues to increase at an annual rate of about 100%. Recently, the information recording capacity exceeding 160 GB per disk has been required for 2.5-inch perpendicular magnetic recording media used in the HDD, etc. and to respond to such a requirement, it is demanded to actualize the information recording density exceeding 250 GB per square inch.
To attain the high recording density in magnetic recording media used in the HDD, etc. perpendicular magnetic recording media by perpendicular magnetic recording system have been proposed in recent years. In the perpendicular magnetic recording system, adjustments are made such that the axis of easy magnetization of the magnetic recording layer is oriented in the perpendicular direction to the substrate surface. The perpendicular magnetic recording system enables the thermal fluctuation phenomenon to be suppressed as compared with the conventional in-plane recording system, and is suitable to introduce high recording densities.
As the magnetic recording media used in the perpendicular magnetic recording system, CoCrPt—SiO2 perpendicular magnetic recording media have been proposed because such media indicate high heat stability and excellent recording properties (for example, Non-patent Document 1). The media are granular type magnetic recording media where in the magnetic recording layer is formed a granular structure that nonmagnetic particle boundary portions are formed between magnetic particles growing continuously in the shape of pillars, and it is intended to both make magnetic particles fine and enhance the coercive force Hc. It is known to use oxides for the nonmagnetic particle boundary (nonmagnetic portion between magnetic particles), and for example, it is proposed to use one of SiO2, Cr2O3, TiO, TiO2, and Ta2O5 (for example, Patent Document 1). However, there is an upper limit in oxides capable of being contained in the particle boundary, and there are also limitations in improvements in fine particles and isolation.
Meanwhile, in order to further enhance the in-plane recording density, proposed also is a method of forming nonmagnetic areas by ion implantation after forming a magnetic layer (for example, Patent Document 2).    Patent Document 1: Japanese Unexamined Patent Publication No. 2006-024346    Patent Document 2: Japanese Unexamined Patent Publication No. 2007-226862    Non-patent Document 1: T. Oikawa et al., IEEE Trans. Magn, vol. 38, 1976-1978 (2002)